Why does the Torah say that Aharon returned to Moshe?
Moshav Zekenim citing R. Yehudah ha'Chasid: He told him that the plague stopped, and Moshe ceased praying. From here, if one was praying for a Choleh and he recovered, he should not cntinue to pray.
Rashi, in Sh'mos 19:8, citing the Pesikta: It is proper for a Shali'ach to return to the Meshale'ach, even if the latter knows what happened! How can we learn this from here? Perhaps here it is extra to teach that one stops praying- Refer to 17:15:151:1. (PF)